Handheld battery powered electronic devices such as tablets and smartphones have been in wide use in recent years, with usage rates that are ever increasing. These electronic devices may be powered off so as to conserve battery life, because insufficient battery life remains to power the device, or because the user is in an area where the use of electronic devices is prohibited.
A common type of voltage regulator used in such electronic devices is known as a low dropout (LDO) regulator, which can operate with a small input to output differential voltage, and which provides a high degree of efficiency and heat dissipation. A typical LDO regulator includes an error amplifier that controls a power field effect transistor (FET). One input of the error amplifier receives a feedback signal, while the other receives a reference voltage. The error amplifier controls the power FET so as to maintain a constant output voltage.
For a variety of reasons, it may be desirable for the error amplifier and power FET to be components having a breakdown voltage that is less than the output voltage of the LDO regulator. Such a design may present challenges when initially powered on, as a failure to provide the full reference voltage (which may not be available immediately after startup) to the error amplifier may result in the error amplifier operating beyond its breakdown voltage, which could result in negative operating characteristics.
Consequently, a LDO regulator design capable of controlling the reference voltage at startup such that the error amplifier does not operate beyond its breakdown voltage is desirable.